The Kevlar is a total marketing ploy. It's not scratch-proof (even bullet resistant Kevlar isn't designed to be stab proof as well), and offers no extra protection (in such a thin layer), over any other standard plastic phone back.

This idea that it's made out of "the same stuff as bullet proof vests", is true, in the same way that the glass in a house window is made from the same stuff that bullet proof glass is made of...strictly true, but also entirely untrue at the same time.

As for Gorilla Glass, it can (and does), scratch and break, it's just a bit tougher than normal glass.

The RAZR is in no way an especially "tough", phone. If you'd stick a Sensation or an S2 in a case (if you had one), put your RAZR in a case. If you wouldn't bother with a case for any other phone, don't bother with the RAZR, simple as that really.